Communication device

ABSTRACT

Improving the accuracy of estimation of channel responses in receiving signals from a plurality of antennas is disclosed. A transmitting device of a base station includes a preamble A generating unit  010 , a preamble B generating unit  011 , phase rotating units  012  and  013 , multiplexing units  014  and  015 , an forward error correction coding unit  016 , an S/P converting unit  017 , a mapping unit  018 , a changeover switch  019 , IDFT (or IFFT) units  020  and  026 , P/S converting units  021  and  027 , GI (Guard Interval) inserting units  022  and  028 , D/A converting units  023  and  029 , radio transmitting units  024  and  030  and antenna units  025  and  031 . In the preamble A generating unit  010  and the preamble B generating unit  011 , a preamble A and a preamble B (see the packet format in FIG.  1 ) are generated, respectively. The preamble A is outputted to the multiplexing units  014  and  015 , while the preamble B is outputted to the phase rotating units  012  and  013 . The phase rotating units  012  and  013  to which the preamble B has been inputted give continuous phase rotation to subcarriers of the preamble B. In the transmitting device of the base station according to this embodiment, the phase rotating unit  012  does not give phase rotation, but only the phase rotating unit  013  gives phase rotation to the preamble B.

TECHNICAL FIELD

The present invention relates to a communication device, andparticularly to a radio transmitting device comprising a plurality ofantennas and to a radio receiving device for receiving signals from theradio transmitting device.

BACKGROUND ART

In recent years, many more users demand fast data transmission in aradio communication system as the volume of communication increases. Themulticarrier transmission represented by OFDM (Orthogonal FrequencyDivision Multiplexing) gets attention as a way of communication torealize the fast and high-volume data transmission. The OFDM, which isused in IEEE 802.11a being a radio system of a 5 GHz-band or digitalterrestrial broadcast, provides for simultaneous communication byarranging tens to thousands of carriers in a minimum frequency intervalthat does not induce interference theoretically. Generally in OFDM,these carriers are referred to as subcarriers which are digitallymodulated with PSK, QAM or the like for communication. It is known thatOFDM and forward error correction are combined to obtain strongtolerance to frequency selective fading.

The configuration of a data packet according to the IEEE 802.11a will bedescribed with reference to FIG. 1. As shown in FIG. 1, a data packetused in the IEEE 802.11a consists of preambles A and B and a datasignal. A preamble A is used for OFDM symbol synchronization andfrequency synchronization, while a preamble B is used for identificationof an antenna and estimation of a channel response. The two preamblesare both predetermined signals, being signals also known to a receivingside.

FIGS. 12 and 13 show configuration examples of an OFDM modulatingcircuit and an OFDM demodulating circuit, respectively. In the drawings,the number of subcarriers in use is defined as N.

FIG. 12 is a functional block diagram of a usual OFDM modulationcircuit. In FIG. 12, reference numeral 1000 denotes an forward errorcorrection coding unit, reference numeral 1001 denotes a serial/parallelconverting unit (S/P converting unit), reference numeral 1002 denotes amapping unit, reference numeral 1003 denotes an IDFT (Inverse DiscreteFourier Transform) unit, reference numeral 1004 denotes aparallel/serial (P/S converting unit), reference numeral 1005 denotes apreamble A generating unit, reference numeral 1006 denotes a preamble Bgenerating unit, reference numeral 1007 denotes a multiplexing unit,reference numeral 1008 denotes a guard interval inserting unit,reference numeral 1009 denotes a digital/analog converting unit (D/Aconverting unit), reference numeral 1010 denotes a radio transmittingunit and reference numeral 1011 denotes an antenna.

Transmitted information data is encoded in the forward error correctioncoding unit 1000. Then, the S/P converting unit 1001 performsserial/parallel conversion on the data by a data amount needed tomodulate each carrier. The mapping unit 1002 modulates each carrier.Afterward, the IDFT unit 1003 performs IDFT. Although an example ofusing IDFT for OFDM modulation is illustrated herein, a general circuitoften defines the number of points in a format 2^(n) and uses the fastinverse Fourier transform (IFFT). In order to generate an OFDM signal ofan N wave, a value 2^(n) not less than N and nearest to N is generallyused as the number of points of IFFT.

After the IDFT, the P/S converting unit 1004 converts the data intoserial data, and then the multiplexing unit 1007 time-multiplexes thedata with the preambles A and B, resulting in the packet configurationshown in FIG. 1. Then, the GI (guard interval) inserting unit 1008inserts a guard interval. A guard interval is inserted to reduceinterference between symbols in receiving an OFDM signal. Further, thedata is converted into an analog signal in the D/A converting unit 1009and then converted into a transmission frequency in the radiotransmitting unit 1010, and finally a packet is transmitted from theantenna 1011.

FIG. 13 is a functional block diagram showing a configuration example ofan OFDM demodulating circuit. As shown in FIG. 13, a receiver conductsreverse processing of the transmission in principle. In FIG. 13,reference numeral 1020 denotes an antenna, reference numeral 1021denotes a radio receiving unit, reference numeral 1022 denotes an A/D(analog/digital) converting unit, reference numeral 1023 denotes asynchronizing unit, reference numeral 1024 denotes a GI removing unit,reference numeral 1025 denotes an S/P converting unit, reference numeral1026 denotes a DFT (Discrete Fourier Transform) unit, reference numeral1027 denotes a changeover switch, reference numeral 1028 denotes apreamble multiplying unit, reference numerals 1029 and 1030 denotemultiplying units, reference numeral 1031 denotes a demapping unit,reference numeral 1032 denotes a P/S converting unit and referencenumeral 1033 denotes an forward error correction decoding unit. However,also a demodulating circuit often uses FFT instead of DFT, as describedabove.

An electric wave received in the antenna unit 1020 isfrequency-converted into a frequency band in which A/D conversion ispossible in the radio receiving unit 1021. The A/D converting unit 1022converts the data into a digital signal, for which the synchronizingunit 1023 conducts OFDM symbol synchronization using the preamble A. TheGI removing unit 1024 removes a guard interval from the data. Afterward,the S/P converting unit 1025 performs serial/parallel conversion on thedata. Then, the DFT unit 1026 performs DFT on the data, the changeoverswitch 1027 transmits the received preamble B subjected to DFT to thepreamble multiplying unit 1028 and transmits the received data signalsubjected to DFT to the multiplying unit 1029. The preamble multiplyingunit 1028 multiplies (multiplies in a frequency domain) a complexconjugate of the received preamble B and the preamble B used in atransmitting side to estimate a channel response. In the following,estimation of a channel response using a preamble (preamble B) being aknown signal and compensation of a channel response will be brieflydescribed using numerical expressions. First, a preamble used in atransmitting side is represented by p(f) and an information signal isrepresented by s(f). Those are expressed as frequency domain signalsherein. Additionally, after transmission of a preamble or an informationsignal, if channel response is defined as c(f), a received preamblep′(f) and a received information signal s′(f) are represented by thefollowing equations. In the equations, c(f) is a complex function togive different amplitude and phase rotation for each subcarrier.

Equation 1p′(f)=c(f)×p(f)  (1)s′(f)=c(f)×s(f)  (2)

However, thermal noise in a receiver is not considered herein forsimplicity. For the receive signals, first, a complex conjugate of p′(f)is obtained in the preamble multiplying unit 1028, and the conjugate ismultiplied by the preamble p(f) used in the transmitting side, asdescribed previously. This multiplication is represented in the equation(3):

$\begin{matrix}{{Equation}\mspace{14mu} 2} & \; \\\begin{matrix}{{p^{\prime}*{(f) \times {p(f)}}} = {c*{(f) \times {p^{*}(f)} \times {p(f)}}}} \\{= {c*{(f) \times {{p(f)}}^{2}}}}\end{matrix} & (3)\end{matrix}$

The output (equation (3)) of the preamble multiplying unit 1028 istransmitted to the multiplying units 1029 and 1030, which multiply theoutput by a received data signal and a received preamble, respectively.An output of the multiplying unit 1029 is shown in the equation (4) andan output of the multiplying unit 1030 is shown in the equation (5):

$\begin{matrix}{{Equation}{\mspace{11mu}\;}3} & \; \\\begin{matrix}{{{{s^{\prime}(f)} \times c}*{(f) \times {{p(f)}}^{2}}} = {{{c(f)} \times c}*{(f) \times {s(f)} \times {{p(f)}}^{2}}}} \\{= {{{c(f)}}^{2}{{{p(f)}}^{2} \times {s(f)}}}}\end{matrix} & (4) \\\begin{matrix}{{{{p^{\prime}(f)} \times c}*{(f) \times {{p(f)}}^{2}}} = {{{c(f)} \times c}*{(f) \times {p(f)} \times {{p(f)}}^{2}}}} \\{= {{{c(f)}}^{2}{{{p(f)}}^{2} \times {p(f)}}}}\end{matrix} & (5)\end{matrix}$

As shown in the equation (4), a received information signal ismultiplied by an output of the preamble multiplying unit 1028, wherebyinfluence of phase rotation by channel response c(f) is compensated anda signal having a phase equal to a transmitted signal s(f) is obtained.Then, the outputs (equations (4) and (5)) of the multiplying units 1029and 1030 obtained in this way are inputted to the demapping unit 1031. Apreamble subjected to channel response compensation in the equation (5)is used as a criterion to demap an information signal for eachsubcarrier. Then, the P/S converting unit 1032 serializes necessarydata, the forward error correction decoding unit 1033 decodes thetransmitted data.

One of examples of aiming fast and high-quality OFDM includes the waydisclosed in the non-patent literature 1. Generally, differentinformation bits are assigned to OFDM subcarriers. However, according tothe non-patent literature 1, an identical information bit is assign toall subcarriers. In order to assign an identical information bit to allsubcarriers in this way and keep a high transmission rate, thenon-patent literature 1 proposes to set a different amount of phaserotation for each information bit and give the phase rotation being setto subcarriers, thereby enabling to assign different information bits toan identical subcarrier for transmission.

FIG. 14 shows a part of transmitter configuration disclosed in thenon-patent literature 1. As shown in FIG. 14, in a transmitting deviceaccording to the non-patent literature 1, an information bit (for BPSKmodulation in the non-patent literature 1) mapped by a mapping unit 1050is copied by the number of subcarriers (the number of subcarriers is Nherein) by copy units 1051 and inputted to subcarrier demodulating andphase rotating units 1052. The subcarrier demodulating and phaserotating units 1052 assign information bits to all subcarriers and givephase rotation being set for each information bit to each subcarrier, asshown in FIG. 14. At that time, continuous phase rotation for adjacentsubcarriers is given such that phase rotation given to the firstsubcarrier of a k-th information bit is 0, while phase rotation given toan n-th subcarrier is (n−1)Δθ_(k). According to the non-patentliterature 1, all of such phase rotation applied subcarriers are added,and outputs of the subcarrier modulating units and the phase rotatingunits for all information bits are further added in an adder 1053. Areceiving device multiplies a complex conjugate of phase rotation givenin a transmitting device, thereby compensating the phase rotation andrestoring information data. The non-patent literature 1 discloses thatit is possible to improve receiving features and ensure a hightransmission rate by such configuration, compared to general OFDM.

-   [Non Patent Literature 1] D. A. Wiegandt, Z. Wu, C. R. Nassar,    “High-throughput, high-performance OFDM via pseudo-orthogonal    carrier interferometry spreading codes”, IEEE Transactions on    Communications, vol. 51, no. 7, July 2003, pp. 1123-1134.

If a plurality of antennas simultaneously transmit differentmulticarrier signals, or if a terminal being positioned around a celledge receives downlink transmission in an OFDM cellular system in whichadjacent cells use an identical frequency band, a plurality of differentmulticarrier signals are mixed in a receiving side, so that therespective signals interfere with each other. In such a case, it is verydifficult to identify which antenna has transmitted a received signal orwhich base station has transmitted the signal. Because of this, therehas been a problem in that the accuracy of estimation of a channelresponse deteriorates significantly.

It is an object of the present invention to improve the accuracy ofestimation of channel responses in receiving signals from a plurality ofantennas.

DISCLOSURE OF THE INVENTION

With radio communication techniques according to the present invention,symbols transmitted simultaneously from a plurality of antennas aregiven different phase rotation for the antennas, whereby a receivingside separates and calculates delay profiles of the signals transmittedfrom the antennas. That is, by transmitting preambles to which differentphase rotation has been applied for a plurality of antennas or cells, areceiving side separates a delay profile of a signal coming from eachantenna or each cell to identify a transmitting antenna or atransmitting base station and to estimate a channel response. If thenumber of delay profiles to be separated is large, different preamblepatterns are used together, realizing highly accurate separation of adelay profile.

Particularly, the techniques can be applied to a case that atransmitting device comprises a plurality of antennas, enablingselection of a transmitting antenna in transmit diversity. Additionally,the number of transmitting antennas in a MIMO (Multi Input Multi Output)system can be decided.

Furthermore, the techniques can be applied to reception of signals froma plurality of transmitting devices. In that case, they can be used toidentify a base station in reception of signals from a plurality of basestations. Further, delay profile separating by time shift and a code canbe used together. That is, the identification of a base station can usea code, while identification of a plurality of antennas in the basestation can use time shift.

The use of the present invention enables to separate and identify OFDMsignals transmitted simultaneously from a plurality of base stations andestimate a channel response of a desired signal with high accuracy. Italso enables to detect a signal of a base station to connect to at thestart of communication and at handover with high accuracy. It furthermakes performing site diversity easy by transmitting identical data froma plurality of adjacent base stations, improving receiving features of aterminal being positioned around a cell boundary. If each base stationcomprises a plurality of transmitting antennas, a sequence of signalspecific to the base station as a signal to estimate a channel responseis used. Then, by giving phase rotation differing among transmittingantennas to the signal to estimate a channel response and bytransmitting the signal, a channel response of a desired signal can beestimated with high accuracy even in the environment in which manysignals are to be separated.

Furthermore, the use of the present invention enables to select anappropriate transmitting antenna or the number of transmitting antennasdepending on the status of a channel response when a transmitting devicecomprising a plurality of transmitting antennas conducts selectivetransmit diversity transmission or MIMO transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a packet format being a targetof radio communication techniques according to embodiments of thepresent invention;

FIG. 2 is a diagram showing a configuration example of a transmittingdevice of a base station among radio communication devices according toa first embodiment of the present invention;

FIG. 3 is a diagram showing a configuration example of a receivingdevice of a terminal according to the first embodiment of the presentinvention;

FIG. 4 is a diagram showing examples of delay profiles obtained by theradio communication technique according to the first embodiment of thepresent invention. FIG. 4(a) is a diagram showing a delay profileobtained in a receiving side when no phase rotation is applied topreambles transmitted from transmitting antennas X and Y. FIG. 4( b) isa diagram showing a delay profile when phase rotation is applied to apreamble transmitted from the transmitting antenna Y;

FIG. 5 is a drawing of an example of cell arrangement being a target ofa radio communication technique according to a third embodiment of thepresent invention;

FIG. 6 is a diagram showing a configuration example of a transmittingdevice of a base station according to the third embodiment of thepresent invention;

FIG. 7 is a functional block diagram showing a configuration example ofa receiving device of a terminal according to the third embodiment ofthe present invention;

FIG. 8 is a diagram showing a problem when a large number of delayprofiles should be separated as an assumption in a radio communicationtechnique according to a fourth embodiment of the present invention;

FIG. 9 is a diagram showing a configuration example of a transmittingdevice according to a second embodiment of the present invention;

FIG. 10 is a diagram showing a configuration example of a receivingdevice according to the second embodiment of the present invention;

FIG. 11 is a diagram showing the flow of transmission and receptionprocessing according to the second embodiment of the present invention;

FIG. 12 is a functional block diagram showing a configuration example ofa usual OFDM modulation circuit;

FIG. 13 is a functional block diagram showing a configuration example ofa usual OFDM demodulating circuit; and

FIG. 14 is a functional block diagram showing a configuration example ofa transmitting device disclosed in the non-patent literature 1.

DESCRIPTION OF SYMBOLS

010 . . . preamble A generating unit; 011 . . . preamble B generatingunit; 012, 013 . . . phase rotating units; 014, 015 . . . multiplexingunits; 016 . . . forward error correction coding unit; 017 . . . S/Pconverting unit; 018 . . . mapping unit; 019 . . . changeover switch;020, 026 . . . IDFT units; 021, 027 . . . P/S converting units; 022, 028. . . GI (Guard Interval) inserting units; 023, 029 . . . D/A convertingunits; 024, 030 . . . radio transmitting units; 025, 031 . . . antennaunits; 040 . . . antenna unit; 041 . . . radio receiving unit; 042 . . .A/D converting unit; 043 . . . synchronizing unit; 044 . . . GI removingunit; 045 . . . S/P converting unit; 046, 052 . . . DFT units; 047 . . .changeover switch; 048 . . . preamble multiplying unit; 049 . . . IDFTunit; 050 . . . delay profile power measuring unit; 051 . . . timefilter; 053 . . . channel response compensation and demapping unit; 054. . . P/S converting unit; 055 . . . forward error correction decodingunit.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is characterized by using a nature that a signalin a time domain can be time-shifted by giving continuous phase rotationto each subcarrier used for multicarrier transmission, to apply atechnique to separate multicarrier signals received via propagationpaths transmitted simultaneously from a plurality of antennas anddiffering among the respective antennas to identification of antennas orbase stations. More specifically, the present invention realizes theabove processing by fixing a phase difference among subcarriers with thesame consecutive preambles, by giving phase rotation of 2mπ (m being aninteger not less than 1) for all subcarriers and by time-shifting asignal for each antenna.

A time-shifted preamble can characteristically serve to estimate channelresponses from antennas using the same code with the same extent ofaccuracy as using different codes. Therefore, shortage of codes can besolved. Further, a single OFDM symbol is sufficient to estimate channelresponses from a plurality of antennas, thereby preventing decrease ofthroughput.

Next, relation between phase rotation given to each subcarrier and timeshift of a signal will be briefly described.

First, a time domain signal is represented by s(t) and a signal obtainedby converting s(t) into a frequency domain one is represented by S(f).The s(t) and S(f) form a Fourier transform pair and have the relation inthe equation (6):

Equation 4s(t)

S(f)  (6)wherein a time shift relation exists that is represented by the equation(7):Equation 5s(t−τ)

S(f)e ^(−j2πfτ)  (7)

As shown in the equation (7), continuous phase rotation in adjacentsubcarriers is given (the right side of the equation (7)), whereby atime domain signal can be time-shifted. Consequently, for example ifsuch phase rotation is applied to a signal (an impulse signal in a timedomain) obtained by setting amplitudes and phases of all subcarriers toequal values, the impulse position can be controlled.

In the following, a system using an OFDM signal being one kind of amulticarrier signal will be described. Such an OFDM system uses 64subcarriers herein.

A packet format for the radio communication techniques according to theembodiments of the present invention is the same as shown FIG. 1 herein.As described previously, a packet shown in FIG. 1 includes a preamble A,a preamble B and data. A preamble A is used for OFDM symbolsynchronization and frequency synchronization, while a preamble B isused for identification of an antenna and estimation of a channelresponse. The two preambles are both predetermined signals.

In the following, the embodiments of the present invention will bedescribed in detail. In the radio communication techniques according tothe following embodiments, discrete Fourier transform and inversediscrete Fourier transform are mainly used as means for performingFourier transform and inverse Fourier transform on a digital signal,while fast Fourier transform and inverse fast Fourier transform can alsobe used. Further, when a transmitting side uses inverse discrete Fouriertransform and a receiving side uses fast Fourier transform, or when atransmitting side uses inverse fast Fourier transform and a receivingside uses discrete Fourier transform, an antenna or a base station canbe identified by giving phase rotation adjusted by considering thenumber of subcarriers in use and the number of points used for fastFourier transform.

First, a radio communication technique according to a first embodimentof the present invention will be described with reference to thedrawings.

The radio communication technique according to the first embodiment ofthe present invention is directed to downlink transmission, in which atransmitting (base station) side comprises a plurality of antennas, andrelates to an antenna selection manner for performing transmittingantenna selection diversity. According to this embodiment, a pluralityof antennas simultaneously transmit OFDM signals, and a receiving sideseparates the signals transmitted from the respective antennas andestimates which antenna has transmitted a received signal having thehighest power.

FIG. 2 is a diagram showing a configuration example of a transmittingdevice of a base station among radio communication devices according tothe first embodiment of the present invention. However, an example isdescribed in which the transmitting device comprises two transmittingantennas in FIG. 2. As shown in FIG. 2, the transmitting device of thebase station according to this embodiment includes a preamble Agenerating unit 010, a preamble B generating unit 011, phase rotatingunits 012 and 013, multiplexing units 014 and 015, an forward errorcorrection coding unit 016, an S/P converting unit 017, a mapping unit018, a changeover switch 019, IDFT (or IFFT) units 020 and 026, P/Sconverting units 021 and 027, GI (Guard Interval) inserting units 022and 028, D/A converting units 023 and 029, radio transmitting units 024and 030, and antenna units 025 and 031.

In the configuration shown in FIG. 2, the preamble A generating unit 010and the preamble B generating unit 011 generate the preamble A and thepreamble B (see the packet format in FIG. 1), respectively. The preambleA is outputted to the multiplexing units 014 and 015, while the preambleB is outputted to the phase rotating units 012 and 013. The phaserotating units 012 and 013, to which the preamble B has been inputted,give continuous phase rotation to subcarriers of the preamble B. In thetransmitting device of the base station according to this embodiment,the phase rotating unit 012 does not give phase rotation, but only thephase rotating unit 013 gives phase rotation to the preamble B. In thisway, phase rotation is given only to the second preamble in a packettransmitted from one antenna of preambles transmitted from the twoantennas that the transmitting device of the base station comprises,while phase rotation is not given to the other preambles. Informationdata is encoded in the forward error correction coding unit 016, goesthrough the S/P converting unit 017 and is mapped depending on amodulation scheme in the mapping unit 018.

An information signal generated in the above way is given phase rotationsimilarly to the preamble B, and then time-multiplexed with the preamblefor transmission. The information signal is transmitted from only anantenna determined to obtain high received power by reflecting a resultof transmitting antenna selection in the previous packet. For thispurpose, a terminal feeds back the result of transmitting antennaselection to the base station. The antenna selection informationreceived in a receiving device 032 of the base station is transmitted tothe changeover switch 019, which performs switching such that aninformation signal is transmitted only from a selected transmittingantenna. However, an information signal is transmitted from any onepredetermined antenna at the start of communication. In the followingdescription, the antenna unit 025 is selected for example.

An antenna for transmitting an information signal is selected asdescribed above, the changeover switch 019 controls the informationsignal to be inputted only to the phase rotating unit 012, and the phaserotating unit 012 gives phase rotation similar to the phase rotationgiven to the preamble B to the information signal (however, as describedabove, the amount of phase rotation given in the phase rotating unit 012is zero in this embodiment). An information signal given phase rotationas described above is time-multiplexed with a preamble in themultiplexing unit 014, and then a guard interval is attached for eachOFDM symbol in the GI inserting units 022 and 028. At that time, the GIinserting unit 022 processes a packet formed by the preambles A and Band an information signal, while the GI inserting unit 028 processes apacket formed by only the preambles A and B. After the guard interval isattached, the antenna unit 025 transmits the packet formed by thepreambles A and B and the information signal at the same time as theantenna unit 031 transmits the packet formed by the preambles A and B,in which both the transmissions are performed through the D/A convertingunits 023 and 029 and the radio transmitting units 024 and 030 providedfor each transmitting antenna.

Next, a configuration example of a receiving device of a terminalaccording to this embodiment will be described with reference to FIG. 3.As shown in FIG. 3, the receiver of the terminal according to thisembodiment includes an antenna unit 040, a radio receiving unit 041, anA/D converting unit 042, a synchronizing unit 043, a GI removing unit044, an S/P converting unit 045, DFT (or FFT) units 046 and 052, achangeover switch 047, a preamble multiplying unit 048, an IDFT (orIFFT) unit 049, a delay profile power measuring unit 050, a time filter051, a channel response compensation and demapping unit 053, a P/Sconverting unit 054 and an forward error correction decoding unit 055.

As described above, a transmitting device of a base stationsimultaneously transmits a packet consisting of preambles A and B and aninformation signal and a packet consisting of preambles A and B fromdifferent antennas. On the other hand, in a receiving device of theterminal, these packets are simultaneously received by the singleantenna 040 via different propagation paths.

The received signal added with the two packets via the differentpropagation paths as above is inputted to the synchronizing unit 043 viathe radio receiving unit 041 and the A/D converting unit 042. In thesynchronizing unit 043, symbol synchronization is established by usingthe preamble A, thereby subsequent processing is performed atappropriate time.

Next, the GI removing unit 044 removes the guard interval attached inthe transmitting side, and then the S/P converting unit 045 converts aserial signal into a parallel signal and inputs the result to the DFTunit 046. Then, the DFT unit 046 converts the received time domainsignal into a frequency domain signal and transmits the result to thechangeover switch 047. The changeover switch 047 controls switching suchthat the preamble B is transmitted to the preamble multiplying unit 048and the information signal is transmitted to the channel responsecompensation and demapping unit 053. Next, the preamble multiplying unit048 multiplies a value obtained by normalizing a complex conjugate ofthe preamble B used in the transmitting side by a squared amplitude ofthe preamble B, and the received preamble B. The received preamble Bindicates a signal added with two preambles B that have been transmittedfrom the two transmitting antennas and have arrived via differentpropagation paths. The multiplication result is converted into a timedomain signal in the IDFT unit 049 to obtain delay profiles ofpropagation paths through which signals have been transmitted from theantenna unit 021 and the antenna unit 029 of the transmitting device ofthe base station. A delay profile obtained herein means an impulseresponse of a propagation path. FIG. 4 shows examples of delay profilesobtained as above. FIG. 4( a) is a diagram showing a delay profileobtained in a receiving side when no phase rotation is applied topreambles transmitted from transmitting antennas X and Y. FIG. 4( b) isa diagram showing a delay profile when phase rotation is applied to apreamble transmitted from the transmitting antenna Y. Detailedconfiguration of the transmitting device and the receiving device isomitted in FIG. 4 for simplicity. FIG. 4 is a drawing showing aconfiguration example in which the receiving device has configurationsimilar to FIG. 3, while the transmitting device does not include aphase rotating unit as in FIG. 4( a) or does include the phase rotatingunit as in FIG. 4( b). Other configuration in FIG. 4 is similar to theconfiguration shown in FIG. 2.

First, as shown in FIG. 4( a), if identical preambles generated by thepreamble B generating unit 011 are simultaneously transmitted from thetwo antennas X and Y of the transmitting device of the base stationshown in the dotted line part in FIG. 2 via propagation paths to thereceiving device, then delay profiles obtained after IDFT (the IDFT unit049 in FIG. 3) in the receiving device are responses added with delayprofiles of the propagation paths through which the signals transmittedfrom the two antennas have been transmitted. As such, in that case, thedelay profiles of the propagation paths through which the signalstransmitted from the two antennas X and Y have been transmitted cannotbe separated for seeking. That is, as can be seen from the relationbetween a delay profile and time, the delay profile of the signaltransmitted from the antenna X shown by solid lines and the delayprofile of the signal transmitted from the antenna Y shown by dottedlines are observed as a composition at a receiving side, so that theycannot be separated.

On the other hand, as shown in FIG. 4( b), if phase rotation is given tosubcarriers of the preamble B generating unit 011 (however, the amountof phase rotation is herein zero in the unit 012 of the phase rotatingunits 012 and 013), then different time shifts are applied to the signaltransmitted from the antenna X and the signal transmitted from theantenna Y according to a principle shown in the equation (7). Because ofthis, at the receiving side, the delay profile of the signal transmittedfrom the antenna X shown by the solid lines and the delay profile of thesignal transmitted from the antenna Y shown by the dotted lines areobserved as two delay profiles being separated in time in the receivingside. In this way, different phase rotation is previously given to asignal transmitted from two antennas at the transmitting side, and thereceiving side performs appropriate time filtering (time filtering todecide time or a sample point to start the filtering depending on theamount of phase rotation given at the transmitting side), thereby adelay profile observed at the receiving side can be easily separated, ascan be seen.

With the radio communication technique according to this embodiment, asdescribed above, a separated delay profile is inputted to the delayprofile power measuring unit 050 shown in FIG. 3, and a transmittingantenna is selected that is observed to have high power of a first-pathelectric wave. For this purpose, selection antenna information that atransmitting antenna is selected that is observed to have high power ofa first-path electric wave in the delay profile power measuring unit 050is inputted to a transmitting device 056 and fed back to the basestation. The selection result is to be reflected in the next downlinktransmission.

A term “first-path electric wave” is herein used in the followingmeaning. That is, usually in a radio communication environment, anelectric wave arrives at a receiver via various routes, so thatdifferent route lengths cause difference of arrival time of the electricwave. In such a multipath environment, an expression “path” generallyrefers to an electric wave (a composite wave of a plurality of electricwaves) that arrives at a certain time, while a “first-path electricwave” means an electric wave that first arrives.

The delay profile obtained in the IDFT unit 049 is inputted to the timefilter 051 and unnecessary portions are removed from the profile. Aninformation signal following the preamble B is transmitted only from oneof the antennas (for example, the antenna unit 021) of the transmittingside. Because of this, in order to compensate a channel response of aninformation signal, it is required to obtain only channel responsebetween an antenna that has transmitted the information signal and thereceiving antenna. Based on this, the time filter 051 (FIG. 2) isconfigured to pass through only a delay profile obtained from thepreamble B transmitted from the same antenna as the information signal,and time or a sample point to start filtering is decided depending onthe amount of phase rotation (the amount of time shift) given at thetransmitting side, as described previously. In this embodiment, sincethe antenna unit 025 has been selected, the amount of phase rotationgiven at the transmitting side is zero, and a reference sample point tostart filtering is also zero. On the contrary, filtering when theantenna unit 031 is selected is started from a reference sample pointnear to applied time shift, while zero is inserted to samples before thereference sample point. An output of the time filter 051 is inputted tothe DFT unit 052, obtaining an estimation value of channel responserequired to demodulate the information signal. Next, the obtainedestimation value of channel response and a received information signalare inputted to the channel response compensation and demapping unit053, which compensates the channel response and demaps the receivedinformation signal. Then, the signal goes through the P/S convertingunit 054 to the forward error correction decoding unit 055 whichperforms decoding, reproducing information data.

Using the above described transmitting device and receiving device, itis possible to separate delay profiles of received signals being OFDMsignals transmitted simultaneously from different antennas that havearrived via different propagation paths, and a single symbol issufficient to precisely estimate channel response and select atransmitting antenna in performing transmit diversity. However, with theradio communication technique according to this embodiment, atransmitting antenna is selected that has power of a first-path electricwave of a delay profile measured to be high; instead, configuration canalso possible in which power of all paths is summed up to select atransmitting antenna having the highest sum total value.

Next, a radio communication technique according to a second embodimentof the present invention will be described with reference to thedrawings. With the above described radio communication techniqueaccording to the first embodiment of the present invention, continuousphase rotation is given to subcarriers used for multicarriertransmission, thereby enabling to time-shift a time domain signal. Usingthis feature, the technique serves to separate multicarrier signalstransmitted simultaneously from a plurality of antennas and received viapropagation paths differing among respective antennas. A relatedtechnique includes a MIMO (Multi Input Multi Output) system as a systemin which a plurality of antennas are used in not only a transmittingside but also a receiving side. The radio communication techniqueaccording to the second embodiment of the present invention is directedto a MIMO system and particularly relates to an approach to decide thenumber of transmitting antennas used in MIMO transmission depending onthe status of a channel response.

First, a configuration example of a transmitting device according to thesecond embodiment of the present invention is shown in FIG. 9. FIG. 9 isa diagram showing a configuration example of a transmitting deviceincluding three transmitting antennas. As shown in FIG. 9, thetransmitting device according to this embodiment includes a preamble Agenerating unit 200, a preamble B generating unit 201, phase rotatingunits 202, 203 and 204, multiplexing units 205, 206 and 207, a datamodulating unit 208, a changeover switch 209, IDFT units 210, 216 and222, P/S converting units 211, 217 and 223, GI inserting units 212, 218and 224, D/A converting units 213, 219 and 225, radio transmitting units214, 220 and 226, and antenna units 215, 221 and 227. As shown in FIG.9, the transmitting device according to this embodiment is configured toselect to perform signal processing on the two preamble generating units200 and 201 and output signals from the preamble generating units 200and 201 directly or through the phase rotating units.

An example of basic data transmission processing in the transmittingdevice shown in FIG. 9 will be described below. In order to start thetransmission processing when information data to be transmitted isgenerated, first, different streams used as the information data aregenerated by the number of antennas, and the data modulating unit 208performs forward error correcting coding or modulation on each datastream. In MIMO transmission to transmit data streams differing amongthe antennas, for example if all of the three antennas are used, tripletransmission capacity can be obtained compared to transmission using asingle antenna. After the modulation in the data modulating unit 208,the changeover switch 209 allocates each stream to the type of anantenna to which the stream is transmitted. Then, the phase rotatingunits 202, 203 and 204 of the types give phase rotation to each streamby the same amount as that of rotation (the amount of phase rotationdiffering among the antenna types) given to the preamble B, and themultiplexing units 205, 206 and 207 time-multiplex the stream with thepreamble A and the preamble B. Afterward, the GI inserting unit attachesa guard interval to a signal subjected to IDFT and P/S conversion in thetypes of antennas. After D/A conversion is further performed on thesignal and the radio transmitting unit performs frequency conversion onthe signal into a radio frequency band, the antenna unit transmitsrespective signal streams.

FIG. 10 is a diagram showing a configuration example of a receivingdevice used in the radio communication technique according to thisembodiment. However, FIG. 10 is a diagram showing an example thatincludes three receiving antennas. As shown in FIG. 10, the receivingdevice according to this embodiment includes antenna units 250, 260 and270, radio receiving units 251, 261 and 271, A/D converting units 252,262 and 272, synchronizing units 253, 263 and 273, GI removing units254, 264 and 274, S/P converting units 255, 265 and 275, DFT units 256,266 and 276, changeover switches 257, 267 and 277, preamble multiplyingunits 258, 268 and 278, IDFT units 259, 269 and 279, a maximum delaytime measuring unit 280 and a demodulating unit 281.

An example of basic data demodulation processing in the transmittingdevice shown in FIG. 10 will be described below. The antenna units 250,260 and 270 shown in FIG. 10 receive signals transmitted from aplurality of antennas included in the transmitting device viapropagation paths. For example, when the three antennas in thetransmitting device transmit different information signal streams, theantenna unit 250 shown in FIG. 10 receives signals in which the threeinformation signal streams through different propagation paths aremixed. Similarly, the antenna units 260 and 270 also receive signals inwhich three information signal streams through different propagationpaths are mixed. On such a received signal, the radio receiving units251, 261 and 271 perform frequency conversion into a frequency band onwhich A/D conversion is possible, the A/D converting units 252, 262 and272 perform A/D conversion, and then the synchronizing units 253, 263and 273 establish OFDM symbol synchronization. The synchronizationprocessing in the synchronizing units 253, 263 and 273 is performedusing the preamble A. Afterward, the GI removing units 254, 264 and 274removes a guard interval, the S/P converting units 255, 265 and 275perform S/P conversion, and then the DFT units 256, 266 and 276 converta received time domain signal into a frequency domain one. Then, thechangeover switches 257, 267 and 277 controls the preamble B to betransmitted to the preamble multiplying units 258, 268 and 278, andcontrols the received information signal to be transmitted to thedemodulating unit 281.

The preamble multiplying units 258, 268 and 278 multiply a valueobtained by normalizing a complex conjugate of the preamble B used inthe transmitting side by a squared amplitude of the preamble B and thereceived preamble B. When the multiplication result is inputted to therespective IDFT units 259, 269 and 279, as described with connection tothe embodiments, delay profiles of propagation paths through whichsignals have been transmitted from the transmitting antennas areobtained in a state being separated for each transmitting antenna. Thisis because the transmitting side gives phase rotation differing amongthe antennas to the preambles, so a time signal time-shifts for eachantenna for the relation in the equation (7). In this way, channelresponse can be compensated for each information signal stream accordingto a delay profile separated for each transmitting antenna. This enablesto demodulate information data in the demodulating unit 281 by realizingthe configuration in which outputs of the IDFT units 259, 269 and 279and information signals received by the receiving antennas are inputtedto the demodulating unit 281.

FIG. 11 is a flowchart showing the flow of the control to change thenumber of antennas for transmitting an information signal streamdepending on the status of a channel response in thetransmitting/receiving devices of a MIMO system including the abovedescribed configuration. First, the flow of the control by thetransmitting side will be described. As shown in FIG. 11 (a; the leftside of the drawing), the transmitting device according to thisembodiment first sets the amount of phase rotating given in the phaserotating unit to zero (without phase rotation) prior to transmission ofa data packet, and transmits a signal consisting of preambles A and Bfrom a single antenna (steps 001 to 002).

Then, as shown at step 003, the receiving device receives theinformation of the number of transmitting antennas fed back from thereceiving side. Next, based on the information of the number oftransmitting antennas received at step 003, the amount of phase rotationgiven to preambles B and information signals transmitted from theantennas is set to values differing among the antennas (step 004), datapackets are transmitted using the number of antennas notified in theinformation of the number of transmitting antennas. However, asdescribed above, information signal streams differing among the antennasare transmitted.

Next, the flow of control processing by the receiving side will bedescribed. As shown in FIG. 11( b), the receiving device according tothis embodiment receives only a signal consisting of a preamble A and apreamble B transmitted from the transmitting side using, for example,three receiving antennas (step 010), performs processing similar to thepreviously described demodulating procedure, and each of the IDFT units259, 269 and 279 calculates a delay profile (step 011). Next, thecalculated delay profile is transmitted to the maximum delay timemeasuring unit 280 shown in FIG. 10, and a delay time τmax of a pathhaving the longest delay time (that arrives last) in all delay profilesis calculated (step 012). Then, as shown at steps 013 and 015, it isdetermined how the τmax accounts for the length of a GI (guardinterval).

At step 013, τmax is compared with GI length*⅓. If it is determined thatτmax is smaller (Yes), the processing proceeds to step 014. If it isdetermined that τmax is larger (No), the processing proceeds to step015. If it is determined that τmax is smaller at step 013, the amount ofphase rotation given to the preambles B transmitted from the threetransmitting antennas is set as follows: for example, the phase rotatingunit 202 sets the amount to 0; the phase rotating unit 203 sets theamount to the phase rotation amount in which the amount of time shift isGI length*⅓; and the phase rotating unit 204 sets the amount to theamount of phase rotation in which the time shift amount is GI length*⅔.By this setting, the delay profiles can be separated without interferingto one another in the receiving side. Consequently, in this processing,information of the number of transmitting antennas is set to 3 as shownat step 014.

Otherwise, if it is determined that τmax is larger at step 013, the useof the three antennas in transmission causes interference among thedelay profiles in the receiving side (see FIG. 8( b)), a channelresponse cannot be estimated correctly. That is, the delay profilestransmitted from the different antennas of the base station cannot beseparated since they interfere with one another. Consequently, in thiscase, transmission using the three antennas is not performed, but theprocessing proceeds to step 015 to compare τmax with GI length*½.

If it is determined that τmax is smaller than GI length*½ at step 015(YES), the amount of phase rotation given to the preambles B transmittedfrom two transmitting antennas is set as follows: for example, the phaserotating unit 202 sets the amount to 0; and the phase rotating unit 203sets the amount to the amount of phase rotation in which the amount oftime shift is GI length*½. By this setting, the delay profiles can beseparated without interfering to one another in the receiving side.Consequently, in this processing, information of the number oftransmitting antennas is set to 2 as shown at step 016. Otherwise, if itis determined that τmax is larger than GI length*½ at step 015 (NO), theuse of the two antennas in transmission causes interference among thedelay profiles in the receiving side (see FIG. 8( b)), a channelresponse cannot be estimated correctly. Consequently, in this case,transmission using the three antennas is not performed, but theprocessing proceeds to step 017 to set the information of the number oftransmitting antennas to 1.

With the above processing, information of the number of transmittingantennas to be fed back to the transmitting side is obtained. Thisenables to feed back the information of the number of transmittingantennas to the transmitting side using a transmitting device 282 of thereceiver (FIG. 10), as shown at step 018. Based on the information ofthe number of transmitting antennas, the transmitting side generates thesame number of information signal streams as the information of thenumber of transmitting antennas and transmits data packets (steps 003 to005), so that the receiving device can receive and demodulate the datapackets (step 019).

As above, the radio communication technique according to this embodimentcan separate a delay profile. Because of this, even in the environmentin which delay time of a delay wave arriving at the receiving devicevaries largely, the appropriate number of transmitting antennas can beselected and channel response can be estimated with high accuracy. Thatis, the technique has an advantage that can realize stable MIMOtransmission. Next, a radio communication technique according to a thirdembodiment of the present invention will be described with reference tothe drawings.

As described above, in the description of the first and secondembodiments of the present invention, an example has been shown that thepresent invention is applied to the configuration in which atransmitting device comprises a plurality of antennas. However, even ifeach of a plurality of transmitting devices use a single antenna, thetransmitting devices are given different phase rotation, so that delayprofiles of signals transmitted from the different transmitting devicescan also be similarly separated and obtained.

The radio communication technique according to the third embodiment ofthe present invention is to use said configuration for identification ofa base station.

First, an example of cell arrangement for the radio communicationtechnique according to this embodiment is shown in FIG. 5. A basestation identification technique will be herein described when aterminal V is positioned at the boundary of cells covered by three basestations S, T and U as shown in FIG. 5. However, all the base stationsare synchronized with one another and an identical frequency is used inall the cells herein.

FIG. 6 is a diagram showing a configuration example of a transmittingdevice of a base station according to this embodiment of the presentinvention. As shown in FIG. 6, a transmitting device of a base stationaccording to this embodiment includes a preamble A generating unit 100,a preamble B generating unit 101, a phase rotating unit 102, amultiplexing unit 103, an forward error correction coding unit 104, anS/P converting unit 105, a mapping unit 106, an IDFT unit 107, a P/Sconverting unit 108, a GI inserting unit 109, a D/A converting unit 110,a radio transmitting unit 111 and an antenna unit 112. Thisconfiguration example is the same as the first embodiment when thenumber of transmitting antennas is one. All of the base stations S, Tand U have the same configuration in this embodiment.

As shown in FIG. 6, the preamble A generating unit 100 and the preambleB generating unit 101 of the base station device according to thisembodiment generate a preamble A and a preamble B, respectively. Thepreamble A is transmitted to the multiplexing unit 103, while thepreamble B is transmitted to the phase rotating unit 102. The phaserotating unit 102 gives continuous phase rotation to subcarriers of thepreamble B, the amount of phase rotation given herein is set to valuesdiffering among the base stations. That is, for example, the basestation S sets the amount of phase rotation to 0, while the base stationT sets the amount to 2mπ and the base station U sets the value to 2nπ,wherein m and n are integers larger than 1 and satisfying m≠n. Theamount of phase rotation is set that differs among base stations asabove, allowing for the terminal to separate delay profiles of signalsarriving from the base stations and to sense a candidate base station tobe connected.

Information data on downlink is transformed to encoded data in theforward error correction coding unit 104 and goes through the S/Pconverting unit 105 to the mapping unit 106 which maps the encoded datadepending on a modulation scheme. However, the information data in theabove description is not data for the terminal V, but controlinformation broadcasted to all the cells or data for terminals alreadyconnected to the base station. The information data generated in thisway is given the same phase rotation as the preamble B in the phaserotating unit 102, and then time-multiplexed with the preamble in themultiplexing unit 103 and transmitted from the antenna unit 112 via theIDFT unit 107, the P/S converting unit 108, the GI inserting unit 109,the D/A converting unit 110 and the radio transmitting unit 111.

Next, a configuration example of a receiving device of a terminalapplied to the radio communication technique according to thisembodiment will be described. FIG. 7 is a functional block diagramshowing a configuration example of a receiving device of a terminalaccording to this embodiment of the present invention. As shown in FIG.7, the receiving device of the terminal according to this embodimentincludes an antenna unit 150, a radio receiving unit 151, an A/Dconverting unit 152, a synchronizing unit 153, a GI removing unit 154,an S/P converting unit 155, a DFT (or FFT) unit 156, a changeover switch157, a preamble multiplying unit 158, an IDFT (or IFFT) unit 159, adelay profile power measuring unit 160 and a demodulating unit 161. Thereceiving device of the terminal shown in FIG. 7 includes almost thesame configuration as the receiving device of the terminal according tothe first embodiment shown in FIG. 3. First, the antenna unit 150simultaneously receives signals transmitted from the base stations S, Tand U. For the received signals in which the signals transmitted fromthe base stations are mixed, synchronization is established in thesynchronizing unit 153 through the radio receiving unit 151 and the A/Dconverting unit 152.

The synchronizing unit 153 establishes synchronization using thepreamble A. Since the preamble A is a common signal to all basestations, synchronization can be established even if signals transmittedfrom the base stations are mixed in. After establishment of thesynchronization, a guard interval of the received signals (the preambleB and information data) is removed in the GI removing unit 154 and thereceived signals go through the S/P converting unit 155 to the DFT unit156 which converts the received signals from time domain signals intofrequency domain signals.

Next, the changeover switch 157 transmits the received preamble B to thepreamble multiplying unit 158 and transmits the received data signals tothe demodulating unit 161. The preamble multiplying unit 158 multipliesa value obtained by normalizing a complex conjugate of the preamble Bused in the transmitting side by the squared amplitude of the preamble Band the received preamble B. The multiplication result is converted intotime domain signals in the IDFT unit 159, obtaining temporally-separateddelay profiles of propagation paths through which signals have beentransmitted from the base stations S, T and U. This separation isrealized by time-shifting the time domain signals for the relation inthe equation (7) by applying different phase rotation to the preambles Bin a frequency domain in the base stations S, T and U. By applying phaserotation in this way to temporally-separated preambles, a delay profilewithout suffering interference from other cells can be obtained.

By measuring a delay profile separated for each base station asdescribed in the above, a base station to be a candidate for a connecteddestination can be sensed. Further, a delay profile separated for eachbase station is transmitted to the delay profile power measuring unit160 and the demodulating unit 161. The delay profile power measuringunit 160 measures and compares power of the first-path electric wave foreach delay profile, and determines which base station has transmitted areceived signal including the highest power. As a result, connection canbe attempted to a base station that has transmitted a received signaldetermined to include the highest power, causing transmission of asignal intended from a transmitting device of a terminal 162 to a basestation. On the other hand, the demodulating unit 161 compensates achannel response using a delay profile separated for each base stationand demodulates information data such as control information.

With the above configuration, the radio communication system accordingto this embodiment can identify a base station to be a candidate for aconnected destination without being influenced by interference fromother cells in an OFDM cellular system in which adjacent cells use anidentical frequency. Additionally, by measuring power of a separateddelay profile, the system can precisely determine a base station to beconnected. Although a base station measured to have high power of thefirst-path electric wave of a delay profile is selected as a basestation being a connected destination in this embodiment, power of allpaths can be summed up to select a base station with the highest sumtotal value.

Also as described above, by simultaneously transmitting preambles givenphase rotation differing among base stations, separated delay profilesof signals transmitted from the base stations can be obtained. Based onthis, if a terminal connected to a base station is positioned around acell edge, it is possible to process so as to calculate delay profilesof signals coming from base stations in adjacent cells and detect a basestation to be a candidate for a handover destination. In this case, abase station that has transmitted a signal to obtain a delay profilewith the highest power is selected as a base station being a handoverdestination among delay profiles other than that of a connected basestation.

Further, in the radio communication system according to this embodiment,a plurality of adjacent base station devices simultaneously transmitdata to a certain terminal, realizing easy performance of site diversity(soft combining reception). This allows improvement of receiving featureof a terminal positioned around a cell boundary.

Next, a radio communication technique according to a fourth embodimentof the present invention will be described with reference to thedrawings. In the third embodiment of the present invention, basestations in a cellular system transmit preambles given different phaserotation, while a receiving side can separate and measure delay profilesof propagation paths through which signals have been transmitted fromthe base stations. The third embodiment is characterized by using thisto select a connected destination base station based on the separatedand measured delay profiles. To apply the characteristics to a system inwhich each base station includes a plurality of antennas, i.e., a systemin which each base station uses a way such as the transmitting antennaselection diversity as shown in the first embodiment, it is required tosimultaneously perform identification of a base station andidentification and selection of a plurality of antennas provided to thebase station. In that case, the number of delay profiles to be separatedequals (the number of base stations)×(the number of antennas in eachbase station), that is, a very large number. When the number of delayprofiles to be separated is large as above, the following problemsarise. The problems will be described with reference to FIG. 8.

As shown in FIG. 8( a), base stations K, L and M are placed in threecells. Each of the base stations K, L and M includes an antenna 1 and anantenna 2. To apply the first embodiment or the third embodimentdescribed previously in the status that a terminal J is positioned inthe vicinity of a boundary among the three cells, phase rotationdiffering among the antennas of the base stations is given to thepreamble B, and the terminal separates delay profiles of propagationpaths through which signals are transmitted from the antennas of thebase stations. If the profiles to be separated and delay waves are manyin the above status, difference in the amount of time shift applied foreach antenna decreases. As such, delay profiles after being separatedmay interfere with one another as shown in FIG. 8( b). In the exampleshown in FIG. 8( b), the last path in a delay profile of a signaltransmitted from the antenna 1 of the base station K interferes with thefirst path in a delay profile of a signal transmitted from the antenna 1of the base station L, while other paths cause interference as shown inFIG. 8( b). If adjacent delay profiles interfere with each other asabove, identification of a base station and selection of an antennacauses a major error. This means that separation is difficult with themethods of separating a delay profile according to the first embodimentand the third embodiment if the number of delay profiles to be separatedis very large. Although the adjacent profiles are represented toslightly overlap to each other on the time axis in the drawing fordescription, they actually completely overlap and are composed.

The radio communication technique according to the fourth embodiment ofthe present invention is characterized by applying a manner ofseparating a delay profile using different preamble patterns toidentification of a base station and selection of an antenna, inaddition to an approach of time-shifting a time domain signal by givingcontinuous phase rotation to subcarriers for the above problems.

In a cellular system according to this embodiment in which each basestation comprises a plurality of antennas, when a terminal separatesdelay profiles of signals transmitted from antennas of base stations,the delay profiles of the base stations are separated depending onpreamble patterns specific to the base stations. The delay profiles ofthe antennas in the base stations is first separated using time shift(the amount of phase rotation) similarly to the third embodiment. Inthis case, the transmitting devices of the base stations are embodied inconfiguration similar to the configuration shown in FIG. 2. However, inthis embodiment, it is necessary to use a pattern specific to a basestation for a preamble B. Additionally, the amount of phase rotation inthe phase rotating units 012 and 013 is required to be set to valuesdiffering among antennas. However, the amount of phase rotation can beset to a common value in a base station.

A receiving device of a terminal according to this embodiment can bealso embodied in the configuration shown in FIG. 7. However, in thisembodiment, the preamble multiplying unit 158 retains a preamble patternfor each base station (a preamble pattern used for each of the basestations K, L and M in the status shown in FIG. 8). A received signal inwhich signals transmitted from base stations are mixed is multiplied byeach preamble pattern to separate a delay profile of each base station.Assuming that there is no correlation among preamble patterns used inthe base stations K, L and M, when the received signal is multiplied bya preamble pattern used in the base station K, delay profiles of signalstransmitted from the base stations L and M are in a noisy waveform andonly a delay profile of a propagation path through which a signal hasbeen transmitted from the two antennas of the base station K is obtainedfrom the IDFT unit 159.

Similarly, when a received signal is multiplied with a preamble patternused in the base station L, only a delay profile of a propagation paththrough which a signal has been transmitted from the two antennas of thebase station L is obtained, while when a received signal is multipliedby a preamble pattern used in the base station M, only a delay profileof a propagation path through which a signal has been transmitted fromthe two antennas of the base station M is obtained. In this way, it ispossible not only to separate a delay profile by giving continuous phaserotation to each subcarrier of a preamble in a transmitting side and byshifting a time waveform, but also to separate a delay profile using adifferent preamble pattern. This enables measuring a delay profile withhigh accuracy, i.e., identification of a base station or selection of anantenna even when there are very many delay profiles to be separatedsuch as when a base station comprises a plurality of antennas.

Additionally, contrary to this embodiment, an approach can also be usedto separate the delay profiles of the base stations by separating delayprofiles of antennas using preamble patterns differing among theantennas and applying time shift differing among base stations topreambles.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a radio communication system.

1. A transmitting device comprising: a phase rotation unit that applies,in a frequency domain and to a sequence which has a code length N andhas a constant amplitude for estimating a channel response, a phaserotation of a rotation amount that is set for the transmitting deviceand that rotates by an integral multiple of 2π at N subcarriers, whereinthe phase difference between adjacent subcarriers is constant; and apreamble generating unit that assigns the sequence for estimating achannel response, to which the phase rotation is applied, to thesubcarriers and transmits the sequence, wherein the transmitting devicereceives information from a receiving device, the transmitting devicedetermines the amount of the phase rotation based on the informationreceived from the receiving device, and a minimum unit of amount of timeshift corresponding to the amount of the phase rotation is a valuegreater than a maximum delay time.
 2. A transmission control method, thetransmission control method comprising: applying, in a frequency domainand to a sequence which has a code length N and has a constant amplitudefor estimating a channel response, a phase rotation of a rotation amountthat is set for a transmitting device and that rotates by an integralmultiple of 2π at N subcarriers, wherein the phase difference betweenadjacent subcarriers is constant; assigning the sequence for estimatinga channel response, to which the phase rotation is applied, to thesubcarriers and transmits the sequence; receiving information from areceiving device; and determining the amount of the phase rotation basedon the information received from the receiving device, wherein a minimumunit of amount of time shift corresponding to the amount of the phaserotation is a value greater than a maximum delay time.
 3. Acommunication system being configured to use a transmission scheme inwhich communication is performed using N subcarriers, the communicationsystem comprising: a transmitting device; and a receiving deviceconfigured to receive signals transmitted from the transmitting device,wherein the transmitting device comprises: a phase rotation unit thatapplies, in a frequency domain and to a sequence which has a code lengthN and has a constant amplitude for estimating a channel response, aphase rotation of a rotation amount that is set for the transmittingdevice and that rotates by an integral multiple of 2π at N subcarriers,wherein the phase difference between adjacent subcarriers is constant;and a preamble generating unit that assigns the sequence for estimatinga channel response, to which the phase rotation is applied, to thesubcarriers and transmits the sequence, wherein the receiving devicereceives the signal transmitted from the transmitting device, thetransmitting device receives information from the receiving device, thetransmitting device determines the amount of the phase rotation based onthe information received from the receiving device, and a minimum unitof amount of time shift corresponding to the amount of the phaserotation is a value greater than a maximum delay time.
 4. A transmittingdevice comprising: a plurality of antennas; a phase rotation unit thatapplies, in a frequency domain and to sequences which has a code lengthN and has a constant amplitude for estimating channel responses, phaserotations of rotation amounts that are set for each antenna of thetransmitting device and that rotates by an integral multiple of 2π at Nsubcarriers, wherein the phase difference between adjacent subcarriersis constant; and a preamble generating unit that assigns the sequencesfor estimating channel responses, to which the phase rotations areapplied, to the subcarriers and transmits the sequences, wherein thetransmitting device receives information from a receiving device, thetransmitting device determines the amounts of the phase rotations basedon the information received from the receiving device, and a minimumunit of amount of time shift corresponding to each amount of phaserotation is a value greater than a maximum delay time.
 5. Thetransmitting device according to claim 4, wherein the sequences arespecific to the transmitting device.
 6. A transmission control method,the transmission control method comprising: applying, in a frequencydomain and to sequences which has a code length N and has a constantamplitude for estimating a channel response, phase rotations of rotationamounts that are set for each antenna of a transmitting device and thatrotates by an integral multiple of 2π at N subcarriers, wherein thephase difference between adjacent subcarriers is constant; assigning thesequences for estimating channel responses, to which the phase rotationsare applied, to the subcarriers and transmits the sequences; receivinginformation from a receiving device; and determining the amounts of thephase rotations based on the information received from the receivingdevice, wherein a minimum unit of amount of time shift corresponding toeach amount of phase rotation is a value greater than a maximum delaytime.
 7. The transmission control method according to claim 6, whereinthe sequences are specific to the transmitting device.
 8. Acommunication system being configured to use a transmission scheme inwhich communication is performed using N subcarriers, the communicationsystem comprising: a transmitting device; and a receiving deviceconfigured to receive signals transmitted from the transmitting device,wherein the transmitting device comprises: a plurality of antennas; aphase rotation unit that applies, in a frequency domain and to sequenceswhich has a code length N and has a constant amplitude for estimatingchannel responses, phase rotations of rotation amounts that are set foreach antenna of the transmitting device and that rotates by an integralmultiple of 2π at N subcarriers, wherein the phase difference betweenadjacent subcarriers is constant; and a preamble generating unit thatassigns the sequences for estimating channel responses, to which thephase rotations are applied, to the subcarriers and transmits thesequences, wherein the receiving device receives the signals transmittedfrom the transmitting device, the transmitting device receivesinformation from the receiving device, the transmitting devicedetermines the amounts of the phase rotations based on the informationreceived from the receiving device, and a minimum unit of amount of timeshift corresponding to each amount of phase rotation is a value greaterthan a maximum delay time.
 9. The communication system according toclaim 8, wherein the sequences are specific to the transmitting device.